The invention relates to the metal production, and more specifically to a method and apparatus for obtaining an ingot.
The invention may be the most advantageously used in casting metal in moulds used in continuous and semicontinuous casting methods, electroslag and vacuum-arc remelting and in other production methods used for making ingots.
Improvement in the quality and structure of an ingot metal is very important in the metal casting technique and obtaining metal having uniform fine-grained structure is not yet completely resolved, especially in the production of heavy-weight castings.
Known in the art are methods of subjecting metals and alloys, in the course of crystallization, to the action of external factors using elastic oscillations provided by ultrasonic oscillations, magnetic field and low-frequency vibrations, and apparatus for effecting these methods.
The method of imparting ultrasonic oscillations to a melt in the course of crystallization has found the widest application.
An apparatus for processing molten metal with ultrasonic oscillations comprises an ultrasonic oscillator having a magnetostriction or piezoelectric converter, an ultrasonic emitter and a resonance tuning system for adjusting natural frequency of molten metal being processed and frequency of induced oscillations of the emitter.
Molten metal is poured into a mould, and the emitter is introduced into the molten metal through a hole in the mould bottom or from the top, through a hole in a mould top.
During the pouring of molten metal into the mould, the ultrasonic oscillator is energized, and ultrasonic oscillations are imparted to the molten metal thus resulting in destruction of growing dendrites and formation of fine-grained structure of the ingot metal. As the natural frequency of the metal (volume) being processed continuously varies during the pouring period, the resonance tuning system is used for automatically maintaining the equality of the natural and induced frequencies of the emitter and melt, respectively. A material disadvantage of this method is that the existing ultrasonic equipment employed for effecting the method has a low output capacity so that large volumes of metal cannot be processed. In addition, low strength of the emitter material does not enable the employment of ultrasonic oscillations for processing high-temperature alloys, such as steel. The provision of the resonance circuit working member/metal in the conditions of variable mass and volume of melt also results in certain technical problems.
It is also known to obtain an ingot using low-frequency vibrations in an apparatus intended for this purpose.
An apparatus for processing molten metal using low-frequency vibrations comprises a mould mounted on a vibrator. The vibrator comprises an electromagnetic system, a cam or eccentric drive, and hydraulic or pneumatic cylinders. Most frequently, the use is made of mechanical vibrators comprising an electric motor connected to a reducing gear and to a shaft journalled in bearings and having an unbalanced flywheel or an eccentric wheel. The shaft is coupled to the reducing gear by means of a clutch. The mould is mounted on the vibrator and filled with molten metal. The electric motor is turned on, and the mould receives oscillations in the vertical plane in accordance with a preset law of oscillations and with a predetermined amplitude and frequency.
It is, however, noted that the resulting elastic oscillations cannot destruct growing metal crystals since the wavelength of induced oscillations of the vibrator is of the order of several scores of meters, whereas the natural frequency of growing metal crystal is in the range of several kHz, that is any resonance is impossible.
Known apparatus designed for imparting elastic oscillations to molten metals provide for varying the oscillation frequency and amplitude in the discrete manner (low-frequency vibrators) or in the stepless manner, but over a very narrow frequency range (ultrasonic oscillators) which constitutes their material disadvantage. Therefore, the above-described methods for obtaining fine-grained uniform ingots have not found wide application in industry, especially in the production of heavyweight ingots.